Interconnect structure and methods thereof

ABSTRACT

A method and structure for forming a local interconnect, without routing the local interconnect through an overlying metal layer. In various embodiments, a first dielectric layer is formed over a gate stack of at least one device and a second dielectric layer is formed over a contact metal layer of the at least one device. In various embodiments, a selective etching process is performed to remove the second dielectric layer and expose the contact metal layer, without substantial removal of the first dielectric layer. In some examples, a metal VIA layer is deposited over the at least one device. The metal VIA layer contacts the contact metal layer and provides a local interconnect structure. In some embodiments, a multi-level interconnect network overlying the local interconnect structure is formed.

PRIORITY DATA

The present application is a continuation application of U.S. patentapplication Ser. No. 16/047,884, filed Jul. 27, 2018, issuing as U.S.Pat. No. 11,222,842, which is a divisional application of U.S. patentapplication Ser. No. 15/253,311, filed Aug. 31, 2016, now U.S. Pat. No.10,276,491, the entire disclosures of which are hereby incorporated byreference in their entireties.

BACKGROUND

The electronics industry has experienced an ever increasing demand forsmaller and faster electronic devices which are simultaneously able tosupport a greater number of increasingly complex and sophisticatedfunctions. Accordingly, there is a continuing trend in the semiconductorindustry to manufacture low-cost, high-performance, and low-powerintegrated circuits (ICs). Thus far these goals have been achieved inlarge part by scaling down semiconductor IC dimensions (e.g., minimumfeature size) and thereby improving production efficiency and loweringassociated costs. However, such scaling has also introduced increasedcomplexity to the semiconductor manufacturing process. Thus, therealization of continued advances in semiconductor ICs and devices callsfor similar advances in semiconductor manufacturing processes andtechnology.

In particular, back-end-of-line (BEOL) fabrication processes havepresented a particularly difficult challenge for advanced ICfabrication. BEOL fabrication includes interconnect structures, forexample, made up of a multi-level network of metal wiring. Any of aplurality of IC circuits and/or devices may be connected by suchinterconnect structures. In various examples, however, interconnectperformance degrades with dimensional scaling. For instance, resistance(R) increases as dimensions get smaller and capacitance (C) increases asa density of interconnects increases, both of which increase RC-delay.In some cases, different materials and/or processes for interconnectfabrication are being studied. In other examples, an increasing numberof metal layers are being used as part of the multi-level interconnectnetwork, to provide additional interconnect routing paths andpotentially reduce R (e.g., by increasing interconnect dimensions)and/or reduce C (e.g., by reducing interconnect density). However,increasing the number of metal layers will invariably increase a totalinterconnect length, which can also degrade device performance.Moreover, the addition of metal layers will lead to an increase in cost(e.g., additional photomasks, design time, etc.).

Thus, existing techniques have not proved entirely satisfactory in allrespects.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when they are read with the accompanying figures.It is noted that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1A is a cross-sectional view of an MOS transistor according to someembodiments;

FIG. 1B is perspective view of an embodiment of a FinFET deviceaccording to one or more aspects of the present disclosure;

FIG. 2 is a flow chart of a method of forming a local interconnect, inaccordance with some embodiments;

FIGS. 3-10 provide cross-sectional views of a device at intermediatestages of fabrication and processed in accordance with the method ofFIG. 2; and

FIGS. 11 and 12 provide layout designs illustrating various aspects ofembodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

It is also noted that the present disclosure presents embodiments in theform of local interconnect structures which may be employed in any of avariety of device types. For example, embodiments of the presentdisclosure may be used to form local interconnect structures in planarbulk metal-oxide-semiconductor field-effect transistors (MOSFETs),multi-gate transistors (planar or vertical) such as FinFET devices,gate-all-around (GAA) devices, Omega-gate (Ω-gate) devices, or Pi-gate(Π-gate) devices, as well as strained-semiconductor devices,silicon-on-insulator (SOI) devices, partially-depleted SOI devices,fully-depleted SOI devices, or other devices as known in the art. Inaddition, embodiments disclosed herein may be employed in the formationof P-type and/or N-type devices. One of ordinary skill may recognizeother embodiments of semiconductor devices that may benefit from aspectsof the present disclosure.

With reference to the example of FIG. 1A, illustrated therein is an MOStransistor 100, providing an example of merely one device type which mayinclude embodiments of the present disclosure. It is understood that theexemplary transistor 100 is not meant to be limiting in any way, andthose of skill in the art will recognize that embodiments of the presentdisclosure may be equally applicable to any of a variety of other devicetypes, such as those described above. The transistor 100 is fabricatedon a substrate 102 and includes a gate stack 104. The substrate 102 maybe a semiconductor substrate such as a silicon substrate. The substrate102 may include various layers, including conductive or insulatinglayers formed on the substrate 102. The substrate 102 may includevarious doping configurations depending on design requirements as isknown in the art. The substrate 102 may also include othersemiconductors such as germanium, silicon carbide (SiC), silicongermanium (SiGe), or diamond. Alternatively, the substrate 102 mayinclude a compound semiconductor and/or an alloy semiconductor. Further,in some embodiments, the substrate 102 may include an epitaxial layer(epi-layer), the substrate 102 may be strained for performanceenhancement, the substrate 102 may include a silicon-on-insulator (SOI)structure, and/or the substrate 102 may have other suitable enhancementfeatures.

The gate stack 104 includes a gate dielectric 106 and a gate electrode108 disposed on the gate dielectric 130. In some embodiments, the gatedielectric 106 may include an interfacial layer such as silicon oxidelayer (SiO₂) or silicon oxynitride (SiON), where such interfacial layermay be formed by chemical oxidation, thermal oxidation, atomic layerdeposition (ALD), chemical vapor deposition (CVD), and/or other suitablemethod. In some examples, the gate dielectric 106 includes a high-kdielectric layer such as hafnium oxide (HfO₂). Alternatively, the high-kdielectric layer may include other high-k dielectrics, such as TiO₂,HfZrO, Ta₂O₃, HfSiO₄, ZrO₂, ZrSiO₂, LaO, AlO, ZrO, TiO, Ta₂O₅, Y₂O₃,SrTiO₃ (STO), BaTiO₃ (BTO), BaZrO, HfZrO, HfLaO, HfSiO, LaSiO, AlSiO,HfTaO, HfTiO, (Ba,Sr)TiO₃ (BST), Al₂O₃, Si₃N₄, oxynitrides (SiON),combinations thereof, or other suitable material. High-K gatedielectrics, as used and described herein, include dielectric materialshaving a high dielectric constant, for example, greater than that ofthermal silicon oxide (˜3.9). In still other embodiments, the gatedielectric 106 may include silicon dioxide or other suitable dielectric.The gate dielectric 106 may be formed by ALD, physical vapor deposition(PVD), CVD, oxidation, and/or other suitable methods. In someembodiments, the gate electrode 108 may be deposited as part of a gatefirst or gate last (e.g., replacement gate) process. In variousembodiments, the gate electrode 108 includes a conductive layer such asW, Ti, TiN, TiAl, TiAlN, Ta, TaN, WN, Re, Ir, Ru, Mo, Al, Cu, Co, CoSi,Ni, NiSi, combinations thereof, and/or other suitable compositions. Insome examples, the gate electrode 108 may include a first metal materialfor an N-type transistor and a second metal material for a P-typetransistor. Thus, the transistor 100 may include a dual work-functionmetal gate configuration. For example, the first metal material (e.g.,for N-type devices) may include metals having a work functionsubstantially aligned with a work function of the substrate conductionband, or at least substantially aligned with a work function of theconduction band of a channel region 114 of the transistor 100.Similarly, the second metal material (e.g., for P-type devices) mayinclude metals having a work function substantially aligned with a workfunction of the substrate valence band, or at least substantiallyaligned with a work function of the valence band of the channel region114 of the transistor 100. Thus, the gate electrode 104 may provide agate electrode for the transistor 100, including both N-type and P-typedevices. In some embodiments, the gate electrode 108 may alternately oradditionally include a polysilicon layer. In various examples, the gateelectrode 108 may be formed using PVD, CVD, electron beam (e-beam)evaporation, and/or other suitable process. In some embodiments,sidewall spacers are formed on sidewalls of the gate stack 104. Suchsidewall spacers may include a dielectric material such as siliconoxide, silicon nitride, silicon carbide, silicon oxynitride, orcombinations thereof.

The transistor 100 further includes a source region 110 and a drainregion 112 each formed within the semiconductor substrate 102, adjacentto and on either side of the gate stack 104. In some embodiments, thesource and drain regions 110, 112 include diffused source/drain regions,ion implanted source/drain regions, epitaxially grown regions, or acombination thereof. The channel region 114 of the transistor 100 isdefined as the region between the source and drain regions 110, 112under the gate dielectric 106, and within the semiconductor substrate102. The channel region 114 has an associated channel length “L” and anassociated channel width “W”. When a bias voltage greater than athreshold voltage (V_(t)) (i.e., turn-on voltage) for the transistor 100is applied to the gate electrode 108 along with a concurrently appliedbias voltage between the source and drain regions 110, 112, an electriccurrent (e.g., a transistor drive current) flows between the source anddrain regions 110, 112 through the channel region 114. The amount ofdrive current developed for a given bias voltage (e.g., applied to thegate electrode 108 or between the source and drain regions 110, 112) isa function of, among others, the mobility of the material used to formthe channel region 114. In some examples, the channel region 114includes silicon (Si) and/or a high-mobility material such as germanium,which may be epitaxially grown, as well as any of the plurality ofcompound semiconductors or alloy semiconductors as known in the art.High-mobility materials include those materials with electron and/orhole mobility greater than silicon (Si), which has an intrinsic electronmobility at room temperature (300 K) of around 1350 cm²/V-s and a holemobility of around 480 cm²/V-s.

Referring to FIG. 1B, illustrated therein is a FinFET device 150,providing an example of an alternative device type which may includeembodiments of the present disclosure. By way of example, the FinFETdevice 150 includes one or more fin-based, multi-gate field-effecttransistors (FETs). The FinFET device 150 includes a substrate 152, atleast one fin element 154 extending from the substrate 152, isolationregions 156, and a gate structure 158 disposed on and around thefin-element 154. The substrate 152 may be a semiconductor substrate suchas a silicon substrate. In various embodiments, the substrate 152 may besubstantially the same as the substrate 102, as described above.

The fin-element 154, like the substrate 152, may include one or moreepitaxially-grown layers, and may comprise silicon or another elementarysemiconductor, such as germanium; a compound semiconductor includingsilicon carbide, gallium arsenide, gallium phosphide, indium phosphide,indium arsenide, and/or indium antimonide; an alloy semiconductorincluding SiGe, GaAsP, AlInAs, AlGaAs, InGaAs, GaInP, and/or GaInAsP; orcombinations thereof. The fins 154 may be fabricated using suitableprocesses including photolithography and etch processes. Thephotolithography process may include forming a photoresist layer(resist) overlying the substrate (e.g., on a silicon layer), exposingthe resist to a pattern, performing post-exposure bake processes, anddeveloping the resist to form a masking element including the resist. Insome embodiments, pattering the resist to form the making element may beperformed using an electron beam (e-beam) lithography process. Themasking element may then be used to protect regions of the substratewhile an etch process forms recesses into the silicon layer, therebyleaving an extending fin 154. The recesses may be etched using a dryetch (e.g., chemical oxide removal), a wet etch, and/or other suitableprocesses. Numerous other embodiments of methods to form the fins 154 onthe substrate 152 may also be used.

Each of the plurality of fins 154 also include a source region 155 and adrain region 157 where the source/drain regions 155, 157 are formed in,on, and/or surrounding the fin 154. The source/drain regions 155, 157may be epitaxially grown over the fins 154. In addition, a channelregion of a transistor is disposed within the fin 154, underlying thegate structure 158, along a plane substantially parallel to a planedefined by section AA′ of FIG. 1B. In some examples, the channel regionof the fin includes a high-mobility material, as described above.

The isolation regions 156 may be shallow trench isolation (STI)features. Alternatively, a field oxide, a LOCOS feature, and/or othersuitable isolation features may be implemented on and/or within thesubstrate 152. The isolation regions 156 may be composed of siliconoxide, silicon nitride, silicon oxynitride, fluorine-doped silicateglass (FSG), a low-k dielectric, combinations thereof, and/or othersuitable material known in the art. In an embodiment, the isolationstructures are STI features and are formed by etching trenches in thesubstrate 152. The trenches may then be filled with isolating material,followed by a chemical mechanical polishing (CMP) process. However,other embodiments are possible. In some embodiments, the isolationregions 156 may include a multi-layer structure, for example, having oneor more liner layers.

The gate structure 158 includes a gate stack having an interfacial layer160 formed over the channel region of the fin 154, a gate dielectriclayer 162 formed over the interfacial layer 160, and a metal layer 164formed over the gate dielectric layer 162. In various embodiments, theinterfacial layer 160 is substantially the same as the interfacial layerdescribed as part of the gate dielectric 106. In some embodiments, thegate dielectric layer 162 is substantially the same as the gatedielectric 106 and may include high-k dielectrics similar to that usedfor the gate dielectric 106. Similarly, in various embodiments, themetal layer 164 is substantially the same as the gate electrode 108,described above. In some embodiments, sidewall spacers are formed onsidewalls of the gate structure 158. The sidewall spacers may include adielectric material such as silicon oxide, silicon nitride, siliconcarbide, silicon oxynitride, or combinations thereof.

As discussed above, each of the transistor 100 and FinFET device 150 mayinclude one or more local interconnect structures, embodiments of whichare described in more detail below. As used herein, the term “localinterconnect” is used to describe the lowest level of metalinterconnects and are differentiated from intermediate and/or globalinterconnects. Local interconnects span relatively short distances andare sometimes used, for example, to electrically connect a source,drain, and/or gate of a given device, or those of nearby devices.Additionally, local interconnects may be used to facilitate a verticalconnection of one or more devices to an overlying metallization layer(e.g., to an intermediate interconnect layer), for example, through oneor more vias. Interconnects (e.g., including local, intermediate, orglobal interconnects), in general, are formed as part ofback-end-of-line (BEOL) fabrication processes and include a multi-levelnetwork of metal wiring. Moreover, any of a plurality of IC circuitsand/or devices (e.g., such as the transistor 100 or FinFET 150) may beconnected by such interconnects.

With the aggressive scaling and ever-increasing complexity of advancedIC devices and circuits, interconnect design and performance has provedto be a difficult challenge. For example, with respect to dimensionalscaling, resistance (R) (e.g., of a given interconnect) increases asdimensions get smaller and capacitance (C) (e.g., of the giveninterconnect) increases as a density of interconnects increases, both ofwhich increase RC-delay. In some examples, additional metal layers havebeen used as part of the multi-level interconnect network, for example,to provide additional interconnect routing paths and potentially reduceR (e.g., by increasing interconnect dimensions) and/or reduce C (e.g.,by reducing interconnect density). For instance, in some cases, localinterconnects may be routed through an overlying metal interconnectlayer. As merely one example, consider a scenario in which one wouldlike to connect a source and a drain of a given device (e.g., such asthe transistor 100 or FinFET 150), for example using a localinterconnect. In at least some existing methods, the local interconnectrouting between the source and drain may go through an overlying metallayer, as discussed above. In short, routing a local interconnectthrough an overlying metal layer is inefficient, costly, and can degradedevice and/or circuit performance. This is demonstrated at least by thefact that increasing the number of metal layers (e.g., to provide theadditional interconnect routing paths), will invariably increase a totalinterconnect length, which can also degrade device performance.Moreover, the addition of metal layers will lead to an increase in cost,for example, due to the need for additional photomasks and increaseddesign time, among other factors. Thus, at least some existing methodsof forming local interconnect have not been entirely satisfactory in allrespects.

Embodiments of the present disclosure offer advantages over the existingart, though it is understood that other embodiments may offer differentadvantages, not all advantages are necessarily discussed herein, and noparticular advantage is required for all embodiments. For example,embodiments discussed herein include methods and structures directed toa local interconnect fabrication process that provides a localinterconnect without routing the local interconnect through an overlyingmetal layer. In particular, and in at least some embodiments, a localinterconnect fabrication process is provided which provides the localinterconnect routing through a VIA layer, without having to utilizeinterconnect layers of the multi-level network of metal wiring. As aresult, and in various embodiments, the number of metal layers used inthe multi-level interconnect network may be reduced. In some examples,the number of metal layers may be reduced at least by one. As a resultof providing the local interconnect routing through the VIA layer,rather than routing through layers of the multi-level interconnectnetwork, the multi-level interconnect network, overlying the localinterconnect, will have improved routing efficiency. Moreover, and incomparison to at least some existing solutions, embodiments disclosedherein reduce cost (e.g., by reduction of a metal layer) and provide forimproved device and/or circuit performance (e.g., by way of a decreasedinterconnect length). It is also noted that the embodiments disclosedherein may be equally applied to both single-height and double-heightcell architectures. Additional details of embodiments of the presentdisclosure are provided below, and additional benefits and/or otheradvantages will become apparent to those skilled in the art havingbenefit of the present disclosure.

Referring now to FIG. 2, illustrated is a method 200 of forming a localinterconnect without routing the local interconnect through an overlyingmetal layer, in accordance with some embodiments. The method 200 isdescribed below in more detail with reference to FIGS. 3-10. The method200 may be implemented on a single-gate planar device, such as theexemplary transistor 100 described above with reference to FIG. 1A, aswell as on a multi-gate device, such as the FinFET device 150 describedabove with reference to FIG. 1B. Thus, one or more aspects discussedabove with reference to the transistor 100 and/or the FinFET 150 mayalso apply to the method 200. To be sure, in various embodiments, themethod 200 may be implemented on other devices such as gate-all-around(GAA) devices, Omega-gate (Ω-gate) devices, or Pi-gate (Π-gate) devices,as well as strained-semiconductor devices, silicon-on-insulator (SOI)devices, partially-depleted SOI (PD-SOI) devices, fully-depleted SOI(FD-SOI) devices, or other devices as known in the art.

It is understood that parts of the method 200 and/or any of theexemplary transistor devices discussed with reference to the method 200may be fabricated by a well-known complementarymetal-oxide-semiconductor (CMOS) technology process flow, and thus someprocesses are only briefly described herein. Further, it is understoodthat any exemplary transistor devices discussed herein may includevarious other devices and features, such as additional transistors,bipolar junction transistors, resistors, capacitors, diodes, fuses,etc., but are simplified for a better understanding of the inventiveconcepts of the present disclosure. Further, in some embodiments, theexemplary transistor device(s) disclosed herein may include a pluralityof semiconductor devices (e.g., transistors), which may beinterconnected. In addition, in some embodiments, various aspects of thepresent disclosure may be applicable to either one of a gate-lastprocess or a gate-first process.

In addition, in some embodiments, the exemplary transistor devicesillustrated herein may include a depiction of a device at anintermediate stage of processing, as may be fabricated during processingof an integrated circuit, or portion thereof, that may comprise staticrandom access memory (SRAM) and/or other logic circuits, passivecomponents such as resistors, capacitors, and inductors, and activecomponents such as P-channel field-effect transistors (PFETs), N-channelFETs (NFETs), metal-oxide-semiconductor field-effect transistors(MOSFETs), complementary metal-oxide-semiconductor (CMOS) transistors,bipolar transistors, high voltage transistors, high frequencytransistors, other memory cells, and/or combinations thereof.

The method 200 begins at block 202 where a substrate having at least onedevice, including a first dielectric layer over a gate stack and asecond dielectric layer over a contact layer, is provided. Withreference to FIG. 3, and in an embodiment of block 202, a substrate 302including a device 304 is provided. In some embodiments, the substrate302 may be substantially the same as either of the substrates 102, 152,described above. It will be understood that the device 304 is merelyillustrative, and is provided for clarity of discussion regardingsubsequent formation of the local interconnect. For example, in somecases, the device 304 may include a planar device, such as thetransistor 100. Alternatively, in some examples, the device 304 mayinclude a multi-gate device, such as the FinFET 150. Moreover, in somecases, the device 304 may include a GAA device, an Ω-gate device, aΠ-gate device, a strained-semiconductor device, an SOI device, a PD-SOIdevice, a FD-SOI device, or other device as known in the art. In someembodiments, the device 304 includes a source 306, a drain 308, and agate stack 310. The device 304 may also include a channel region betweenthe source 306 and the drain 308, under the gate stack 310, and withinthe substrate 302. In various embodiments, the gate stack 310 mayinclude an interfacial layer formed over the channel region, a gatedielectric layer formed over the interfacial layer, and a metal layerformed over the gate dielectric layer. In some embodiments, each of theinterfacial layer, the dielectric layer, and the metal layer of the gatestack 310 may be substantially the same as those described above withrespect to the transistor 100 and the FinFET 150.

As shown in FIG. 3, the device 304 may further include a firstdielectric layer 312 over the gate stack 310. In some embodiments, thefirst dielectric layer 312 includes SiO_(x), SiN, SiO_(x)N_(y),SiC_(x)N_(y), SiO_(x)C_(y)N_(z), AlO_(x), AlO_(x)N_(y), AlN, HfO, ZrO,HfZrO, CN, poly-Si, combinations thereof, or other suitable dielectricmaterial. The first dielectric layer 312 may be formed by ALD, PVD, CVD,oxidation, and/or other suitable methods. In some examples, the firstdielectric layer 312 may have a thickness in a range of about 5-25nanometers. As discussed in more detail below, the first dielectriclayer 312 separates the gate stack 310 from the subsequently formedlocal interconnect. In various embodiments, sidewall spacers 314 aredisposed on the sidewalls of the gate stack 310 and the first dielectriclayer 312. In some embodiments, the sidewall spacers 314 includeSiO_(x), SiN, SiO_(x)N_(y), SiC_(x)N_(y), SiO_(x)C_(y)N_(z), AlO_(x),AlO_(x)N_(y), AlN, HfO, ZrO, HfZrO, CN, poly-Si, combinations thereof,or other suitable dielectric material. In some embodiments, the sidewallspacers 314 include multiple layers, such as main spacer walls, linerlayers, and the like. By way of example, the sidewall spacers 314 may beformed by depositing a dielectric material over the device 304 andanisotropically etching back the dielectric material. In someembodiments, the etch-back process (e.g., for spacer formation) mayinclude a multiple-step etching process to improve etch selectivity andprovide over-etch control.

Additionally, in some embodiments, an inter-layer dielectric (ILD) layer316 is formed over the device 304. By way of example, the ILD layer 316may include materials such as tetraethylorthosilicate (TEOS) oxide,un-doped silicate glass, or doped silicon oxide such asborophosphosilicate glass (BPSG), fused silica glass (FSG),phosphosilicate glass (PSG), boron doped silicon glass (BSG), and/orother suitable dielectric materials. The ILD layer 316 may be depositedby a subatmospheric CVD (SACVD) process, a flowable CVD process, orother suitable deposition technique. In some cases, a contact etch stoplayer (CESL) may be deposited prior to deposition of the ILD layer 316.

In various embodiments, contact openings are then formed (e.g., withinthe ILD layer 316, and in some cases, a portion of the sidewall spacers314). For example, source/drain contact openings may be formed toprovide access to the source and drain 306, 308. By way of example, thesource/drain contact openings may be formed by a suitable combination oflithographic patterning and etching (e.g., wet or dry etching)processes. Thereafter, a source/drain contact metal is formed within thesource/drain contact openings, thereby providing an electricalconnection to the source and drain 306, 308. In particular, as shown inthe example of FIG. 3, a source/drain contact metal 318 is formed, forexample by a suitable combination of layer deposition (e.g., PVD, ALD,CVD), lithographic patterning and etching (e.g., wet or dry etching)processes. In some embodiments, the source/drain contact metal 318includes Ti, W, Co, Cu, Al, Mo, MoW, W, TiN, TaN, WN, silicides,combinations thereof, or other suitable conductive material. In someexamples, the device 304 may further include a second dielectric layer320 over the source/drain contact metal 318. In some embodiments, thesecond dielectric layer 320 includes SiO_(x), SiN, SiO_(x)N_(y),SiC_(x)N_(y), SiO_(x)C_(y)N_(z), AlO_(x), AlO_(x)N_(y), AlN, HfO, ZrO,HfZrO, CN, poly-Si, combinations thereof, or other suitable dielectricmaterial. The second dielectric layer 320 may be formed by ALD, PVD,CVD, oxidation, and/or other suitable methods. In some examples, thesecond dielectric layer 320 may have a thickness in a range of about5-25 nanometers. In some embodiments, a chemical mechanicalplanarization (CMP) process may be performed to remove excess materialand planarize the top surface of the device 304.

It is noted that conventionally, a conductive layer may be formed overthe source/drain contact metal 318 immediately after formation of thesource/drain contact metal 318. Initial formation of the seconddielectric layer 320 over the source/drain contact metal 318, and laterremoval as discussed in more detail below, enables subsequent formationof the local interconnect, in accordance with embodiments of the presentdisclosure.

The method 200 proceeds to block 204 where a third dielectric layer isdeposited over the at least one device. With reference to FIG. 4, and inan embodiment of block 204, a third dielectric layer 402 is formed overthe device 304. In some embodiments, the third dielectric layer 402includes SiO_(x), SiN, SiO_(x)N_(y), SiC_(x)N_(y), SiO_(x)C_(y)N_(z),AlO_(x), AlO_(x)N_(y), AlN, HfO, ZrO, HfZrO, CN, poly-Si, combinationsthereof, or other suitable dielectric material. The third dielectriclayer 402 may be formed by ALD, PVD, CVD, oxidation, and/or othersuitable methods. In some examples, the third dielectric layer 402 mayhave a thickness in a range of about 5-25 nanometers.

The method 200 then proceeds to block 206 where the third dielectriclayer is patterned. With reference to FIGS. 4 and 5, and in anembodiment of block 206, the third dielectric layer 402 is patterned bya photolithography and etching process. As part of the patterningprocess, and in various embodiments, a photoresist layer 502 may firstbe deposited over the third dielectric layer 402 (e.g., by spin-oncoating). In some examples, a hard mask layer may optionally bedeposited over the third dielectric layer 402, with the photoresistlayer 502 then formed over the hard mask layer. In embodiments includinga hard mask layer, the hard mask layer may include a suitable dielectricmaterial, such as silicon nitride, silicon oxynitride or siliconcarbide, or other appropriate material. The hard mask layer may beformed by ALD, PVD, CVD, and/or other suitable methods. In someexamples, after forming the photoresist layer 502, additionalphotolithography steps may include soft baking, mask aligning, exposure,post-exposure baking, developing, rinsing, drying (e.g., spin-dryingand/or hard baking), other suitable lithography techniques, and/orcombinations thereof. As a result of the photolithography process, apattern is formed within the photoresist layer 502, where such a patternmay then be used as a mask to etch the underlying third dielectric layer402. In particular, and as shown in FIG. 5, an etching process isperformed to etch the third dielectric layer 402, thereby transferringthe pattern of the photoresist layer 502 to the third dielectric layer402 and forming a slot 504. In various embodiments, the etching processmay include a dry etching process (e.g., RIE or ICP etching), a wetetching process, or a combination thereof. It is also noted that theetching process employed may include a selective etching process, suchas a selective wet or selective dry etching process, that provides forremoval of desired portions of the third dielectric layer 402, withoutsubstantial removal of other layers that may be exposed to the etchingprocess (e.g., the first dielectric layer 312, the sidewall spacers 314,and/or the second dielectric layer 320). In addition, the slot 504 maybe patterned in a variety of sizes, in accordance with a particularapplication, technology, or other process requirement. By way ofexample, in some cases, the slot 504 may be patterned to have a slotlength ‘L’ equal to about 40-80 nanometers and a slot width ‘W’ equal toabout 5-20 nanometers. Other slot geometries are likewise envisioned asfalling within the scope of this disclosure, as discussed in more detailbelow with reference to FIGS. 11 and 12. In various embodiments, thepatterning of the slot will determine, at least in part, a size (e.g.,length and width) of the subsequently formed local interconnect, asdiscussed below.

The method 200 then proceeds to block 208 where the second dielectriclayer is etched. Additionally, in various examples, the photoresistlayer 502 is removed after patterning the third dielectric layer 402(block 206) and prior to etching the second dielectric layer 320 (block208). With reference to FIGS. 5 and 6, and in an embodiment of block208, the second dielectric layer 320 is etched to form openings 602 andthereby provide access to the source/drain contact metal 318. Inparticular, in various embodiments, the second dielectric layer 320 maybe etched using a selective etching process, such as a selective wet orselective dry etching process, that provides for removal of the seconddielectric layer 320, without substantial removal of other layers thatmay be exposed to the etching process (e.g., the first dielectric layer312, the sidewall spacers 314, and/or the third dielectric layer 402).

In some embodiments, the second dielectric layer 320 and the thirddielectric layer 402 may include different materials that are notequally etched by a given wet or dry etching process. In such cases, themethod 200 may proceed as described above, with distinct etchingprocesses for each of the second dielectric layer 320 and the thirddielectric layer 402. However, in some cases, the second dielectriclayer 320 and the third dielectric layer 402 may include the samematerial, or materials that are substantially equally etched by a givenwet or dry etching process, such that a single etching process may beused to etch the third dielectric layer 402 and the underlying seconddielectric layer 320. Regardless of whether a single etching process ordistinct etching processes are used to etch the second dielectric layer320 and the third dielectric layer 402, the process includes a selectiveetching process that does not substantially remove at least the firstdielectric layer 312 and the sidewall spacers 314.

The method 200 then proceeds to block 210 where a metal layer isdeposited and a CMP process is performed. Referring to FIG. 7, and in anembodiment of block 210, a metal layer 702 is deposited by ALD, PVD,CVD, and/or other suitable method. By way of example, the metal layer702 includes a blanket layer of metal deposited over the device 304. Insome embodiments, the metal layer 702 includes Ti, W, Co, Cu, Al, Mo,MoW, W, TiN, TaN, WN, silicides, combinations thereof, or other suitableconductive material. As shown in FIG. 7, the deposited metal layer 702fills the slot 504 and the openings 602 and contacts the source/draincontact metal 318 over each of the source 306 and the drain 308, therebyelectrically connecting the source 306 and the drain 308 of the device304 and thus providing a local interconnect. In addition, the firstdielectric layer 312 separates, and in some cases electrically isolates,the gate stack 310 from the metal layer 702 that provides the localinterconnect. With reference to FIG. 8, and also in an embodiment ofblock 210, a CMP process is performed to remove excess material (e.g.,excess material of the metal layer 702) and planarize the top surface ofthe device 304. In various examples, the metal layer 702 includes alayer conventionally used as a VIA (e.g., that would conventionallyconnect the source/drain contact metal 318 to an overlying metal layerthat is part of a conventional multi-level interconnect network).However, in accordance with embodiments of the present disclosure,rather than routing through such an overlying metal layer, the localinterconnect is provided through a VIA layer (e.g., the metal layer702), without having to utilize an overlying metal layer. Thus, routingefficiency is improved, a number of required metal layers is reduced(e.g., at least by one metal layer), cost is reduced, and deviceperformance is improved.

The method 200 proceeds to block 212 where a fourth dielectric layer isdeposited over the at least one device. With reference to FIG. 9, and inan embodiment of block 212, a fourth dielectric layer 902 is formed overthe device 304, including over the metal layer 702 that provides thelocal interconnect. In some embodiments, the fourth dielectric layer 902includes SiO_(x), SiN, SiO_(x)N_(y), SiC_(x)N_(y), SiO_(x)C_(y)N_(z),AlO_(x), AlO_(x)N_(y), AlN, HfO, ZrO, HfZrO, CN, poly-Si, combinationsthereof, or other suitable dielectric material. The fourth dielectriclayer 902 may be formed by ALD, PVD, CVD, oxidation, and/or othersuitable methods. In some examples, the fourth dielectric layer 902 mayhave a thickness in a range of about 5-25 nanometers.

The method 200 proceeds to block 214 where a multi-level interconnectnetwork is formed over the fourth dielectric layer. With reference toFIGS. 9 and 10, and in an embodiment of block 214, a multi-levelinterconnect network 1002 is formed over the fourth dielectric layer902. In some cases, the multi-level interconnect network 1002 includesintermediate and global interconnects, while local interconnects areprovided in accordance with embodiments of the present disclosure (e.g.,such as described for the local interconnect provided by the metal layer702). In some embodiments, the multi-level interconnect network 1002 mayinclude various metal layers/lines, vias, interlayer dielectrics, and/orother appropriate features. The multi-level interconnect network 1002may, at various locations throughout the substrate, connect to the localinterconnect provided by the metal layer 702, for example, by way of oneor more VIAs passing through the fourth dielectric layer 902, and toprovide electrical contact to the device 304 or other devices formed inthe substrate 302. In general, the multi-level interconnect network 1002may be configured to connect various devices (e.g., such as the device304) or other features/devices to form a functional circuit that mayinclude one or more planar MOSFETs and/or FinFET devices. In furtheranceof the example, the multi-level interconnect network 1002 may includevertical interconnects, such as vias or contacts, and horizontalinterconnects, such as metal lines. The various interconnection featuresmay employ various conductive materials including copper, tungsten,and/or silicide. In at least one example, a damascene and/or dualdamascene process is used to form a copper-containing multi-levelinterconnect network 1002.

While an example of the method 200 was described above as providing alocal interconnect that electrically connects a device source and drain(e.g., the source 306 and the drain 308 of the device 304), it will beunderstood that this example is not meant to be limiting in any way. Forinstance, embodiments of the present disclosure may be implemented toprovide local interconnects that are used, for example, to electricallyconnect a source, drain, and/or gate of a given device, or those ofnearby devices, and/or to connect to other nearby active and/or passivedevices and/or features. Additionally, embodiments of the presentdisclosure may be used to provide local interconnects which facilitate avertical connection of one or more devices to an overlying metallizationlayer (e.g., through a dielectric layer and to the multi-levelinterconnect network 1002), for example, through one or more vias. Asmerely a few examples, a local interconnect as described herein mayconnect a source of a given device to a drain of a neighboring device, agate of a given device to a source or drain of the given device, asource/drain/gate of a given device to a VIA that further connects thesource/drain/gate of the given device to an overlying metal layer, orany of a plurality of other possible local interconnect connections. Inaddition, the various embodiments disclosed herein may be utilized, forexample, in conjunction with any of a variety of device types such as aplanar device (e.g., the transistor 100), a multi-gate device (e.g., theFinFET 150), a GAA device, an Ω-gate device, a Π-gate device, astrained-semiconductor device, an SOI device, a PD-SOI device, a FD-SOIdevice, or other device as known in the art. Moreover, additionalprocess steps may be implemented before, during, and after the method200, and some process steps described above may be replaced oreliminated in accordance with various embodiments of the method 200.

To elaborate further on the above discussion, reference is now made toFIGS. 11 and 12, which provide layout designs that illustrate variousaspects of embodiments of the present disclosure. Referring first toFIG. 11, a layout design 1102 includes active region layers 1104, gateregion layers 1106, local interconnect layers 1108, 1109, gate contactlayers 1110, drain contact layers 1112, and a first layer of amulti-level interconnect network 1114. In some embodiments, the localinterconnect layers 1108, 1109 represent local interconnects that may beformed as described above, and thus may for example include the metallayer 702. As shown in the example of FIG. 11, the local interconnectlayers 1108, 1109 each extend over a single gate region layer 1106within the active region layer 1104. Thus, the local interconnect layers1108, 1109 may also be used to connect the source and drain of a givendevice, as described above. FIG. 11 also provides additional detailregarding local interconnect size (e.g., length and width). In oneexample, the local interconnect layers 1108, 1109 may be patterned tohave a length ‘L’ equal to about 40-80 nanometers and a width ‘W’ equalto about 5-20 nanometers, similar to the slot size discussed above withreference to FIG. 5 and the slot 504. As noted above, the patterning ofthe slot will determine, at least in part, a size (e.g., length andwidth) of the subsequently formed local interconnect (e.g., the localinterconnect layers 1108, 1109).

With reference to FIG. 12, a layout design 1202 is provided. The layoutdesign 1202 is substantially similar to the layout design 1102; however,the layout design 1202 provides a local interconnect layer 1108A thatmay be used instead of the local interconnect layer 1108. In someembodiments, the local interconnect layer 1108A may be formed asdescribed above, and thus may for example include the metal layer 702.As shown in the example of FIG. 12, the local interconnect layer 1108Aextends over three gate regions 1106 within the active region 1104. Inthe example illustrated, the local interconnect layer 1108A may be usedto connect the source and drain of a plurality of devices, or only thesource and/or drain of selected devices over which the localinterconnect layer 1108A spans, as well as for example the drain contactlayer 1112. Generally, the local interconnect layers 1108, 1108A, or1109, like the slot 504 discussed above with reference to FIG. 5, may bepatterned in a variety of sizes, in accordance with a particularapplication, technology, or other process requirement. As merely oneexample, FIG. 12 illustrates an embodiment where the local interconnectlayer 1108A is shown to be patterned to have a length equal to about2.5× the length of the local interconnect layer 1108. Thus, in someexamples, the local interconnect layer 1108A may have a length ‘L’ equalto about 100-200 nanometers. Restating the above, in a broader sense,various embodiments of the local interconnects may be patterned to havea length ‘L’ equal to about 40-200 nanometers and a slot width ‘W’ equalto about 5-20 nanometers.

The various embodiments described herein offer several advantages overthe existing art. It will be understood that not all advantages havebeen necessarily discussed herein, no particular advantage is requiredfor all embodiments, and other embodiments may offer differentadvantages. As one example, embodiments discussed herein include methodsand structures directed to a local interconnect fabrication process thatprovides a local interconnect without routing the local interconnectthrough an overlying metal layer. In particular, and in at least someembodiments, a local interconnect fabrication process is provided whichprovides the local interconnect routing through a VIA layer, withouthaving to utilize interconnect layers of the multi-level network ofmetal wiring. As a result, and in various embodiments, the number ofmetal layers used in the multi-level interconnect network may be reduced(e.g., at least by one layer). Thus, the various embodiments disclosedherein provide for improved interconnect routing efficiency, a reductionin the required number of metal layers, cost reduction, and improveddevice and circuit performance.

Thus, one of the embodiments of the present disclosure described amethod for fabricating a semiconductor device, where the method includesforming a first dielectric layer over a gate stack of at least onedevice and a second dielectric layer over a contact metal layer of theat least one device. In various embodiments, a selective etching processis performed to remove the second dielectric layer and expose thecontact metal layer, without substantial removal of the first dielectriclayer. In some examples, a metal VIA layer is deposited over the atleast one device. The metal VIA layer contacts the contact metal layerand provides a local interconnect structure. In some embodiments, amulti-level interconnect network overlying the local interconnectstructure is formed.

In another of the embodiments, discussed is a method where a deviceincluding a gate stack having a first dielectric layer formed thereon isprovided. In some embodiments, a source and a drain are formed on eitherside of the gate stack. Additionally, and in various examples, a contactmetal layer is disposed over the source and the drain, and a seconddielectric layer is formed over the contact metal layer. By way ofexample, a third dielectric layer may be formed over the device and afirst etching process of the third dielectric layer may be performed. Inparticular, the first etching process defines a slot within the thirddielectric layer. Thereafter, in some embodiments, a second etchingprocess is performed to remove the second dielectric layer and formopenings that expose the contact metal layer over each of the source andthe drain. In some examples, a conductive layer is deposited over thedevice, and within each of the slot and the openings. The conductivelayer contacts the contact metal layer over each of the source and thedrain.

In yet another of the embodiments, discussed is a semiconductor deviceincluding a substrate with a device having a gate stack and source/drainregions formed on either side of the gate stack. In some embodiments, afirst dielectric layer is formed over the gate stack, and a contactmetal is formed over the source/drain regions. By way of example, athird dielectric layer may also be formed over the device, where thethird dielectric layer includes a slot defined therein. In someembodiments, a metal VIA layer is disposed over the device, where themetal VIA layer contacts the contact metal over both of the source/drainregions and provides a local interconnect between the source/drainregions. In addition, and in some embodiments, the metal VIA layer isseparated from the gate stack by the first dielectric layer. In variousexamples, a multi-level interconnect network may be disposed over themetal VIA layer, where a fourth dielectric layer interposes the metalVIA layer and the multi-level interconnect network.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor device, comprising: a gate stackand source/drain regions formed on either side of the gate stack; afirst dielectric layer formed over the gate stack, and a contact metalformed over the source/drain regions; a local interconnect that contactsthe contact metal over each of the source/drain regions to provide anelectrical connection therebetween, wherein the local interconnect isseparated from the gate stack by the first dielectric layer, whereinfirst portions of the local interconnect disposed over the source/drainregions have first bottom surfaces that are substantially level with asecond bottom surface of the first dielectric layer, and wherein asecond portion of the local interconnect disposed over the gate stackhas a third bottom surface that is substantially level with a third topsurface of the first dielectric layer.
 2. The semiconductor device ofclaim 1, wherein a first top surface of the gate stack defines a firstplane, and wherein a second top surface of the contact metal defines asecond plane that is substantially level with the first plane.
 3. Thesemiconductor device of claim 1, further comprising: a second dielectriclayer disposed over the semiconductor device, wherein the seconddielectric layer includes a slot defined therein, and wherein the localinterconnect is disposed within the slot.
 4. The semiconductor device ofclaim 1, further comprising: sidewall spacers disposed on sidewalls ofthe gate stack and the first dielectric layer.
 5. The semiconductordevice of claim 1, wherein the local interconnect includes Ti, W, Co,Cu, Al, Mo, MoW, W, TiN, TaN, WN, silicides, or combinations thereof. 6.The semiconductor device of claim 1, further comprising: a multi-levelinterconnect network disposed over the local interconnect, wherein athird dielectric layer interposes the local interconnect and themulti-level interconnect network.
 7. The semiconductor device of claim3, wherein the first dielectric layer includes a first material and thesecond dielectric layer includes a second material different than thefirst material.
 8. The semiconductor device of claim 3, wherein the slothas a slot length equal to about 40-80 nanometers and a slot width equalto about 5-20 nanometers.
 9. The semiconductor device of claim 2,wherein lateral end portions of the local interconnect extend down tothe second top surface of the contact metal on opposing sides of thefirst dielectric layer.
 10. A semiconductor device, comprising: a firstdielectric layer formed over a gate stack and a contact metal layerformed over each of a source region and a drain region disposed onopposing sides of the gate stack; and a metal layer that electricallyconnects the contact metal layer over the source region to the contactmetal over the drain region, wherein a middle portion of the metal layeris electrically isolated from the gate stack by the first dielectriclayer, and wherein end portions of the metal layer contacting the sourceregion and the drain region are laterally separated from the firstdielectric layer by sidewall spacers disposed on sidewalls of the gatestack; wherein a first top surface of the gate stack defines a firstplane, wherein a second top surface of the contact metal layer over thesource region defines a second plane substantially coplanar with thefirst plane; and wherein a third top surface of the contact metal layerover the drain region defines a third plane substantially coplanar withboth the first plane and the second plane.
 11. The semiconductor deviceof claim 10, wherein the first dielectric layer has a first width, andwherein the gate stack has a second width that is substantially equal tothe first width.
 12. The semiconductor device of claim 10, furthercomprising: a multi-level interconnect network disposed over the metallayer, wherein another dielectric layer interposes the metal layer andthe multi-level interconnect network.
 13. The semiconductor device ofclaim 10, wherein the sidewall spacers are disposed on the sidewalls ofthe gate stack and on sidewalls of the first dielectric layer.
 14. Thesemiconductor device of claim 10, wherein the metal layer includes Ti,W, Co, Cu, Al, Mo, MoW, W, TiN, TaN, WN, silicides, or combinationsthereof.
 15. The semiconductor device of claim 10, further comprising: asecond dielectric layer formed over the semiconductor device, whereinthe second dielectric layer includes a slot defined therein, and whereinthe metal layer is disposed within the slot.
 16. The semiconductordevice of claim 15, wherein the first dielectric includes a firstmaterial and the second dielectric includes a second material differentthan the first material.
 17. The semiconductor device of claim 10,wherein the metal layer has a length equal to about 40-80 nanometers anda width equal to about 5-20 nanometers.
 18. A method of semiconductordevice fabrication, comprising: forming a first dielectric layer over agate stack of at least one device and a second dielectric layer over acontact metal layer of the at least one device, wherein a first topsurface of the gate stack defines a first plane; performing a selectiveetching process to remove the second dielectric layer and expose thecontact metal layer, without substantial removal of the first dielectriclayer, wherein the exposed contact metal layer includes a second topsurface that defines a second plane substantially coplanar with thefirst plane; and forming a local interconnect structure over the atleast one device, wherein the local interconnect structure contacts thecontact metal layer.
 19. The method of claim 18, further comprising:forming a third dielectric layer over the local interconnect structure;and forming a multi-level interconnect network over the third dielectriclayer.
 20. The method of claim 18, wherein the first dielectric layerelectrically isolates the gate stack from the local interconnectstructure, and wherein the contact metal layer is disposed over asource/drain region.